Industrial spark ignited engines with a power output below approximately 25 horsepower are used as a power source for a wide variety of disposable goods such as go carts, lawn mowers and industrial equipment including generator sets, compressors, pumps, and so on. The raw exhaust emissions from these engines, which are available in one or two cylinder configurations, are extremely high, not only because of poor performance dictated by low cost engineering and manufacturing, but also because of the fundamental necessity of operation with rich air fuel ratios dictated by the use of air cooling instead of water cooling. To illustrate how high the emissions are from these engines, a typical 4 horsepower lawn mower engine for example generates as much carbon monoxide in one hour of operation as an average 1990's automobile engine driven approximately 350 miles.
Conventional application of catalyst technology in the exhaust stream of these engines offers moderate but short lived benefits due to sintering of the precious metal support at the high temperatures of operation. Raw exhaust temperatures of these engines are typically 700 to 800.degree. C., and these temperatures are further increased by the exothermic oxidation reaction.
These engines also produce high vibration levels due to unbalanced inertia forces typical of one or two cylinder configurations, which lead to fatigue cracks on any auxiliary heavy parts attached to the engines and especially exhaust components such as catalyst converter systems because of the high temperatures of operation.